Vehicle internal combustion engines (ICE) generally comprise accessories that are used in the operation of the engine and vehicle. Such accessories can include a power steering pump, an air conditioning compressor, an alternator, an oil pump, a fuel pump and so on. These accessories are generally driven by a serpentine belt. The serpentine belt engages a pulley on each accessory as well as on an engine crankshaft. The engine crankshaft provides the torque to drive the accessories.
As the belt is driven by the crankshaft it is necessarily subject to engine speed variations during acceleration and deceleration of the vehicle. In other words the operating speed of the accessories is directly proportional to the speed of the engine.
The variations in engine speed, particularly engine speeds greater than idle, result in inefficient operation of the accessories because each accessory must be designed to operate satisfactorily over the entire engine speed range. This necessarily means that the efficiency is less than optimum for most of the engine speed range. Further, at higher engine speeds greater power is required to drive the accessories, resulting in reduced fuel efficiency and reduced available torque. Therefore it is desirable to decouple some or all of the accessories from the engine crankshaft so they can be driven at a lower and narrower optimum speed range.
Additionally, the ICE will need to operate at all times to drive these accessories. Utilizing a belt starter generator (BSG) in conjunction with a two speed belt drive system allows for the ICE to be turned off during events when only accessories need to be driven providing significant fuel economy savings.
Representative of the art is U.S. Pat. No. 7,798,928 which discloses a dual ratio belt drive system comprising a clutch unit mounted directly to a driver rotating shaft, a one-way clutch mounted directly to the driver rotating shaft, a plurality of rotating accessories rotatably connected to the clutch unit and rotatably connected to the driver rotating shaft through the one-way clutch such that the accessories are driven by the clutch unit at a first speed ratio and driven directly by the driver rotating shaft through said one-way clutch at a second speed ratio, with the clutch unit operating at a predetermined value of an engine operating condition thereby defining the transition between the first and second speed ratios, and the clutch unit being engaged at engine start.
What is needed is a starter generator system configured to be driven by the engine through a second belt or to drive the engine through a second belt according to an engine condition, and an accessory engaged with the second belt through an accessory clutch, the accessory drivable by a first belt or the second belt. The present invention meets this need.